1. Field of the Invention
This invention relates to a process for preparing metal oxides or metal aquoxides that are dispersible in organic solvents. The invention further relates to metal oxides or metal aquoxides that are modified with organic sulfonic acids and can be prepared by this process.
2. Description of the Prior Art
From WO 95/12547 or German patent DE 43 37 643-C1, a process is known for the preparation of nanocrystalline alumina hydrates in boehmitic or pseudoboehmitic form that are dispersible in water. Water-dispersible alumina hydrates can be obtained in this process by hydrolysis of aluminum alkoxides at temperatures from 30° C. to 110° C., addition of an acid (monovalent inorganic or organic acids as well as their anhydrides), and subsequent hydro-thermal aging. The resultant suspensions are suitable for example for coating materials, such as glass, metal, or plastics, as well as for producing high-strength catalyst supports, pure-phase mixed oxides, or after conversion to the α-form, for producing high-performance abrasives. The water-dispersibility of those alumina hydrates, which are not dispersible in organic solvents, is a disadvantage for certain applications, such as weather-resistant exterior coatings. For certain applications, aluminas that are dispersible in organic solvents but not in water are of interest.
The aluminas prepared by some of the processen known in the art are dispersible in dilute acids and water, and some of these aluminas are dispersible in short-chain alcohols, such as methanol and ethanol. They are not dispersible in organic aprotic solvents.
Colloidal alumina solutions in organic solvents are described for example in DE 41 16 522-C2 as well as by R. NaB and H. Schmidt (“Formation and Properties of Chelated Aluminum Alkoxides” in H. Hauener, G. Messing, S. Hirano (Eds.) “Ceramic Powder Processing”, Deutsche Keramiache Geaellachaft, Cologne, 1969). According to said publication, the alumina hydrates obtained by hydrolysis of aluminum alkoxides in an organic solvent and in the presence of a β-diketone compound can occur as colloids in the solvent. However, the colloidal solutions described there are only (meta)stable in the organic solvent at high dilutions. Only for isopropanol as a solvent has it been experimentally proven that the solutions are in fact colloidal ones. Experiments have shown that after removal of the solvent, the colloidal particles prepared by said process cannot be redispersed.
From AU 200149 a process is known for the preparation of various inorganic oxides and hydroxides that can be dispersed in mineral oils. For this purpose, inorganic oxides or hydroxides are subjected to grinding in a ball mill in the presence of a surfactant and a mineral oil as the carrier fluid. As surfactants, organic sulfonic acids are cited among others. The surfactants are added to the composition in quantities of 0.5 to 3 wt. %.
In U.S. Pat. No. 3,018,172, a process is described for the preparation of aluminum hydroxides that are dispersible in non-polar, high-molecular organic solvents, such as mineral oils. In said process, aluminum alkoxides in a volatile organic solvent are hydrolyzed by contact with an organic sulfonic acid, such as postdodecylbenzenesulfonic acid in a viscous organic carrier fluid. After hydrolysis, the volatile organic solvent is removed and an aluminum hydroxide dispersed in a viscous organic carrier fluid, such as xylene, remains.
A similar process is described in U.S. Pat. No. 3,867,296, wherein a high-molecular organic sulfonic acid in a viscous organic carrier fluid is added to alumina hydrates in a volatile organic medium.
U.S. Pat. No. 4,076,638 and U.S. Pat. No. 4,123,231 describe variants of this process. According to U.S. Pat. No. 4,076,638, a carboxylic acid is used in parallel, while the viscous organic carrier fluid is dispensed with. According to U.S. Pat. No. 4,123,231, an aqueous mineral acid is used in addition to the organic sulfonic acid.